Method of making an electrochromic layer and new electrochromic device made therefrom

ABSTRACT

This invention teaches an electrochromic device in which an electrochromic layer is positioned between two electrodes. The electrochromic layer comprises an inorganic based bulk material supporting electrochromic particles and ion producing particles in fixed but generally distributed positions therewithin. The bulk material permits migration of ions produced by the ion producing particles to and from the electrochromic particles upon change in voltage between the first and second electrodes. The bulk material also prohibits the passage of electrons therethrough when a voltage is applied between the first electrode and the second electrode, whereby an electric field is built up between the first and second electrodes which causes migration of the ions. A preferred method of making a material which can form an electrochromic layer is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of making an electrochromic layer anda new electrochromic device made therefrom.

2. Description of the Related Art

In order to better understand my inventive contributions, I will firstundertake a general discussion of electrochromic behavior inelectrochromic materials. Electrochromism is a coloring phenomenonobserved in some materials when they are placed in the presence of anelectrical field. Such materials are normally uncolored when noelectrical field is present, but change to a colored state when anelectrical field is placed therearound.

Such a material exhibiting reversible color changes is known as anelectrochromic material (ECM). This electrical field dependenttransition phenomenon from an uncolored state to a colored state iscalled optical switching. If a thin coating of such an ECM is placed ona glass support, the entire device is known as a switchable window. Whenno electrical field is placed on the ECM, it is uncolored andtransparent and thus one can look through the window. On the other hand,when an electric field is placed on the ECM, it colors thereby reducingthe amount of light transmitted through the window. The reduction oflight transmission may be partial or total thereby either reducing theamount of light which passes through the window or eliminating italtogether.

Certain transition metal oxides are known to exhibit electrochromism.Materials such as tungsten oxide, molybdenum oxide, and vanadium oxideare known electrochromic materials.

Electrochromic materials can be divided into two categories depending onthe mode of operation of the ECM. The ECM can be either a cathodic ECMor it can be an anodic ECM. The operation of these two types of ECM willbe understood by reference to FIGS. 1 and 2.

In FIG. 1, the operation of a cathodic ECM is schematically illustrated.In the cathodic case, an electrochromic material of the cathodic type isphysically located next to a cathode which has been placed, for example,on a glass substrate. A fast ion conductor material, which produceslight ions of a positive charge, for example, lithium ions, is placedbetween the electrochromic material and an anode which also may beplaced on a glass substrate.

In the cathodic case, the electrochromic material is subjected to areduction or gain of electrons when an electric field is appliedthereto. Application of the electric field is indicated by the pluralityof plus signs shown on the anode and the plurality of negative signsshown on the cathode. As a result of the application of an electricfield applied between the anode and the cathode of appropriate strengthand sign, positive light ions are driven from the fast ion conductorinto the electrochromic material and electrons are supplied to theelectrochromic material from the cathode.

The positively charged light ions and the negatively charged electronsassociate themselves with the electrochromic material to reduce the samethereby moving the electrochromic material from a base state to areduced state. In the base state, the electrochromic material isuncolored, but in its reduced state, it is colored.

When the electric field is removed, the electrochromic material willreturn to its base state, that is, its uncolored state. The period oftime required for return of the material to its uncolored state variesfrom material to material and is generally referred to as the memory ofthe ECM. Some materials have relatively short memories and others haveprolonged memories.

While the operation of the cathodic material has been illustrated by theinclusion in the electrochromic material of positive light ions andnegative electrons, the cathodic operation may also take place by theextraction of negative light ions and holes from the electrochromicmaterial respectively to the fast ion conductor and the cathode.

Operation of an anodic ECM is schematically illustrated in FIG. 2. Inthis case, the electrochromic material is located next to the anode andthe fast ion conductor is located between the electrochromic materialand the cathode. In the anodic operation, oxidation of the ECM takesplace, that is, electrochromism occurs when the ECM loses electrons. Theloss of electrons in this case is illustrated by the application of anelectric field represented by a plurality of pluses on the anode and theplurality of minuses at the cathode.

In the case of an anodic ECM, when an electric field is applied betweenthe anode and the cathode of appropriate strength and sign, negativelight ions, such as hydroxyl ions, move from the fast ion conductor intothe ECM, and holes moves into the ECM from the anode. As a result ofthis movement, the ECM loses electrons thereby being oxidized away fromits base or uncolored state to a colored state. Once again, the anodicmaterial will return to its base state when the electric field isreleased. The time of return to its uncolored state again depends on thememory of the ECM.

The anodic ECM may also operate by extracting from the ECM positivelight ions and negative electrons respectively to the fast ion conductorand the anode. In this case, the ECM is also oxidized to a coloredstate.

In general, in either the cathodic ECM or the anodic ECM, the coloringobserved in the material is an electrochemical phenomenon produced bythe application of an electric field on the ECM to move it from a basecondition to a nonbase condition. By applying a field of requiredstrength and direction to cause activity in the ECM, polarization occurswithin the entire electrochromic device. In such polarization, adisassociation of ions occurs in the fast ion conductor creating freelight ions of the required charge. These light ions move into the ECMbecause of the electrical field. Once in the ECM, they bond themselvesto the molecules of the ECM.

As has been described above, depending on the charge of the bonding ionand its associated electron or hole, oxidation or reduction of the ECMoccurs. These ECM materials are normally multivalent state materialsexhibiting different optical absorption and dispersion spectracorresponding to different oxidation states. For these ECM's, thesedifferent oxidation and reduction states are all stable underappropriate electric field conditions.

In the base ECM, the metal valance states are generally at the maximum,whereby such metal oxides in their base state exhibit the lowest opticalabsorption. They are generally good insulators with high energy gaps,optically transparent and colorless in such a condition. On the otherhand, oxygen deficient oxides as well as reduced oxides created as aresult of the application of electric field exhibit higher opticalabsorption than those of base oxides. When oxygen deficient, ECM'sexhibit a selective absorption when they are in one of their otheroxidation states. Different ECM exhibit different colors, depending uponthe spectral location of the selective absorption bands of thatparticular oxygen deficient metal oxide.

The explanation so far set forth above of cathodic and anodic ECM is mybest explanation. It is possible to reduce this theory of mine toelectrochemical equations in which a base ECM, acting as a cathodicmaterial, would be subjected to a reduction by inclusion in the ECM ofpositive light ions and negative electrons or by extraction from the ECMof negative light ions and holes respectively to the fast ion conductorand the cathode in order to reduce the cathodic ECM to its coloredstate.

In a similar manner, an electrochemical equation may be written for ananodic ECM in the same manner. In this case, the inclusion of negativelight ions and holes in the ECM or the extraction of positive light ionsand negative electrons respectively to the fast ion conductor and theanode is sufficient to oxidize the anodic material to a colored state.

I personally conducted a search in the U.S. Patent and Trademark Officeon the subject matter of this specification. As a result of that search,I uncovered only two patents which I felt were remotely associated withthe subject matter to be taught as the invention herein. The patentswere U.S. Pat. Nos. 4,298,448, and 4,652,090.

U.S. Pat. No. 4,298,448 issued on Nov. 3, 1981 for an "ElectrophoreticDisplay". This patent discloses an electrophoretic display including acell having two plates spaced apart and provided at least regionallywith electrodes. At least one of the plates and an associated electrodefacing an observer are transparent. The cell contains a suspensionconsisting of an inert dielectric liquid phase and a dispersed solidphase which at least in part are optically discriminate electrophoreticparticles. The individual electrophoretic particles each are ofpractically the same density as the liquid phase. At least some of theelectrophoretic particles are provided with a coating of organicmaterial which is solid at the cell operating temperature but whichmelts at higher temperatures. The coating contains at least one chargecontrol agent, preferably a salt of a divalent metal or metal of highervalency and of an organic acid, which imparts a well defined, uniformsurface charge and a well defined, uniform surface potential to theparticles. In essence, this patent teaches a very difficult to prepareelectrophoretic display device.

U.S. Pat. No. 4,652,090 issued on Mar. 24, 1987 for a "Dispersed IridiumBased Complementary Electrochromic Device". This patent discloses anelectrochromic device including one electrode layer, a cathodicallycoloring electrochromic layer, an ion conductive layer if required, areversibly oxidizable layer and another electrode layer. At least one ofthe electrode layers is transparent. At least one of the cathodicallycoloring electrochromic layer, the ionic conductive layer and thereversibly oxidizable layer is adapted to contain protons or include aproton source for emitting protons upon application of a voltage. Thereversibly oxidizable layer comprises a transparent dispersion layerwhich is made by vacuum thin film formation techniques of thick-filmprocesses and comprises a metal iridium, iridium oxide or iridiumhydroxide disperse phase and a transparent solid dispersion medium. Asan alternate, the reversibly oxidizable layer and the other electrodeare replaced with a single transparent conductive dispersion materiallayer which is made by vacuum thin film formation techniques ofthick-film formation techniques or thick-film processes and comprises ametal iridium iridium oxide or iridium hydroxide disperse phase and atransparent solid dispersion medium.

It is an object of this invention to provide a new electrochromicdevice.

It is a feature of this invention that a new electrochromic device isprovided in which both electrochromic particles and ion producingparticles are supported in the same matrix.

It is an advantage of this invention that a new electrochromic device isprovided in which both electrochromic particles and ion producingparticles are supported in the same matrix.

It is another object of this invention to provide a method of making anelectrochromic layer.

It is another feature of this invention to provide a method of making anelectrochromic layer in which both electrochromic particles and ionproducing particles are supported in the same matrix.

It is another advantage of this invention that a method is provided formaking an electrochromic layer in which both electrochromic particlesand ion producing particles are supported in the same matrix.

DISCLOSURE OF THE INVENTION

This invention is directed to a new electrochromic device. In accordancewith the invention the device has a first and a second electrode. Anelectrochromic layer is located between the first and the secondelectrodes. The electrochromic layer comprises an inorganic based bulkmaterial supporting electrochromic particles and ion producing particlesin fixed but generally distributed positions therewithin. The bulkmaterial permits migration of ions produced by the ion producingparticles to and from the electrochromic particles upon change involtage between the first and second electrodes. The bulk material alsoprohibits the passage of electrons therethrough when a voltage isapplied between the first electrode and the second electrode, whereby anelectric field is built up between the first and second electrodes whichcauses migration of the ions.

In accordance with details of preferred embodiments of the invention,one or both of the electrodes are transparent electrodes. Preferably theinorganic based bulk material includes aluminum oxide, or tantalumoxide, or silicon oxide, or a mixture of two or more of these compounds.The electrochromic particles may be anodic electrochromic particles orcathodic electrochromic particles or even mixtures of the two types ofelectrochromic particles. Preferably, all of the anodic or cathodicelectrochromic particles are the same.

Also in accordance with my invention, a method of making a materialwhich can form an electrochromic layer is taught. The method has thefollowing steps. An inorganic based material, electrochromic particlesand ion producing particles are mixed together and then applied to oneof the electrodes by thermally evaporating the mixture in a vacuum ofabout 10⁻⁴ torr. The mixture is spaced from the electrode it is to coatby a distance of about l0 cm. The inorganic based material is one whichpermits migration of ions therethrough but prohibits passage ofelectrons therethrough. In such a manner a inorganic bulk materialsupporting electrochromic particles and ion product particles in fixedbut generally distributed positions therewithin, whereby anelectrochromic device is prepared.

In accordance with details of preferred embodiments of the invention,the inorganic based bulk material includes aluminum oxide, or tantalumoxide, or silicon oxide, or mixtures of two or more of these compounds.The electrochromic particles may be anodic electrochromic particles orcathodic electrochromic particles or even mixtures of the two types ofelectrochromic particles. Preferably, all of the anodic or cathodicelectrochromic particles are the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects, features and advantagesthereof, will best be understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings in which:

FIGS. 1 and 2, as previously discussed, are schematic illustrationsrespectively of the operation of a cathodic electrochromic device and ofan anodic electrochromic device.

FIG. 3 is a schematic illustration of an operational mode of anelectrochromic device in accordance with this invention.

FIGS. 4 and 5 are enlarged schematic illustrations of a matrix materialused in the electrochromic device of FIG. 3 showing in FIG. 4 the matrixmaterial without an electric field applied thereto and in FIG. 5 thematrix material with an electric field applied thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is what I consider to be the preferredembodiments of my invention. The following description also sets forthwhat I now contemplate to be the best mode of construction for aninventive electrochromic device. The description is not intended to be alimitation upon the broader principles of this invention.

FIGS. 3 through 5 schematically illustrate the electrochromic device ofmy invention. FIG. 4 illustrates the matrix material with no electricfield present and FIG. 5 illustrates the matrix material with anelectric field present. The electrochromic device may be fabricated tohave anodic electrochromic properties or cathodic electrochromicproperties, or both, as desired.

Reference is now made to FIG. 3. In this preferred embodiment, an anodicECM is disclosed. A first glass sheet has an anode thereon and a secondglass sheet has a cathode thereon. In both cases, in accordance with thepreferred embodiment of my invention, the glass sheets have a thicknessof 1/8 inch and the electrodes have a thickness of about 2000 angstroms.In accordance with the teachings of the preferred embodiment, both theanode and the cathode are formed from tin oxide doped with fluorine.Such a coating may be applied to the glass sheet by a pyrolytic process,as is well-known in the art. It is, of course, apparent that otherelectrode materials may be used and other materials may be substitutedfor the glass sheets, for example, quartz, plastic, etc. Generally, one,or both, of the electrode supports should be transparent so that thecolors developed in the electrochromic material may be viewed.

As shown in FIG. 3 in the preferred embodiment, a matrix material isprovided that supports therein both finely divided ion producingmaterial and finely divided electrochromic material between the cathodeand the anode. An example of the preparation of a matrix materialsupporting therein both finely divided ion producing material and finelydivided electrochromic material is set forth below.

EXAMPLE

The matrix material was prepared by mixing on a volume basis 1% LiCl,the ion producing material, 60% Al₂ O₃, the inorganic based bulkmaterial, and 39% WO₃, the electrochromic material. This mixture wasloaded into a tantalum boat which was heated to a temperature below theevaporation of the mixture for one-half hour to insure that thecompounds forming the mixture are in their base state. The temperatureof the mixture is then raised to its evaporation temperature and thethermal evaporation was carried out at a pressure of approximately 10⁻⁴torr of vacuum. The mixture was placed about 10 cm from the electrode tobe coated.

In this manner, the inorganic based bulk material supportingelectrochromic particles and ion producing particles in fixed butgenerally distributed positions therewithin was applied to theelectrode. After this preparation, a second electrode was applied to theexposed inorganic based bulk material to form an electrochromic device.

As stated above, the finely divided electrochromic material added to themixture was WO₃. The amount of WO₃ added to the mixture is the amount ofWO₃ that would be required to produce a layer having a thickness of 4000A° on one of the electrodes. A range of WO₃ additions would besufficient WO₃ to produce a layer having a thickness in a range from3000 A° to 5000 A°. The electrochromic WO₃ is a cathodic electrochromicmaterial.

The inorganic based bulk matrix material supporting therein the finelydivided ion producing material and the finely divided electrochromicmaterial in fixed but generally distributed positions is then positionedbetween the two electrodes as is shown in FIG. 3. The matrix materialhas a thickness which depends on the type of material used and the typeof materials added thereto. In the preferred case, the matrix has athickness of about 6000 A°. Since WO₃ is a cathodic material, when anegative five volts was applied between the anode and the cathode, ablue color resulted in the electrochromic device.

The production of the blue color may be explained by aid of FIGS. 4 and5. FIG. 4 shows a schematic illustration of the matrix containing thefinely divided ion producing material and the finely dividedelectrochromic material in a condition where no voltage is applied tothe anode and the cathode of the electrochromic device of FIG. 3. Inthis case the electrochromic particles do not have a charge associatedtherewith and the ions, both positive and negative, are randomlypositioned.

When the voltage is applied to the electrochromic device as describedabove, then the electrochromic particles do have a charge (polarizationphenomenon) associated therewith as shown in FIG. 5 by the plus andminus signs on the electrochromic particles. When this charging occurs,positive light ions drifting due to the applied field are drawn to thenegative end of the electrochromic particles and negative light ions aredrawn to the positive end of the electrochromic particles. This actioncauses a reduction of the electrochromic WO₃ and results in theproduction of the blue color.

In accordance with the teachings of this invention, various materialsmay be used to form the inorganic bulk material. For example, aluminumoxide, or tantalum oxide, or silicon oxide, or other known solid ionconductors, or a mixture of two or more of these compounds may be used.The electrochromic particles may be made from any suitableelectrochromic material or mixtures of such materials. The ion producingparticles also may be selected from any material which produces thedesired ions. Other deposition techniques can be used to produce matrixelectrochromic layers than the illustrated thermal evaporationtechnique. For example, such techniques as sputtering, spray, sol-gel,CVD, or other known techniques can be employed the form the matrixelectrochromics.

While the above Example shows the use of a cathodic electrochromicparticles embedded in the matrix, it is possible to embed both cathodicand anodic particles in the matrix at the same time. If this is done, itis preferred that the two types of particles have about the sameswitching times between their uncolored and colored states. Also, ifjust anodic or cathodic particles are to be used, the particles may bemixtures of various types of anodic or cathodic particles. Again, it ispreferred that the various types of particles have about the sameswitching times between their uncolored and colored states.

While particular embodiments of the invention have been illustrated anddescribed, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from theinvention, and it is intended to cover in the appended claims all suchmodifications and equivalents as fall within the true spirit and scopeof this invention.

I claim:
 1. An electrochromic device which comprises:a first electrode;a second electrode; an electrochromic layer between said first and saidsecond electrodes comprising: an inorganic based solid materialsupporting electrochromic particles and ion producing particles in fixedbut generally distributed positions therewithin, said solid materialpermitting migration of ions produced by said ion producing particles toand from said electrochromic particles upon change in voltage betweensaid first and second electrodes, said solid bulk material alsoprohibiting the passage of electrons therethrough when a voltage isapplied between said first electrode and said second electrode, wherebyan electric field is built up between said first and second electrodeswhich causes migration of said ions.
 2. The electrochromic device ofclaim 1 wherein: one of said first or second electrodes is a transparentelectrode.
 3. The electrochromic device of claim 1 wherein: both saidfirst and said second electrodes are transparent electrodes.
 4. Theelectrochromic device of claim 3 wherein: said inorganic based materialincludes aluminum oxide.
 5. The electrochromic device of claim 3wherein: said inorganic based solid material includes tantalum oxide. 6.The electrochromic device of claim 3 wherein: said inorganic based solidmaterial includes silicon oxide.
 7. The electrochromic device of claim 1wherein: said electrochromic particles are anodic electrochromicparticles.
 8. The electrochromic device of claim 7 wherein: said anodicelectrochromic particles are all the same.
 9. The electrochromic deviceof claim 1 wherein: said electrochromic particles are cathodicelectrochromic particles.
 10. The electrochromic device of claim 9wherein: said cathodic electrochromic particles are all the same. 11.The electrochromic device of claim 1 wherein: said electrochromicparticles are a mixture of both anodic and cathodic electrochromicparticles.
 12. The electrochromic device of claim 11 wherein: saidanodic electrochromic particles are all the same and said cathodicelectrochromic particles are all the same.
 13. A method of making amaterial which can form an electrochromic layer which comprises thesteps of:applying an inorganic solid material permitting the migrationof ions therethrough but prohibiting the passage of electronstherethrough, electrochromic particles, and ion producing particles toan electrode by thermally evaporating a mixture of said inorganic solidmaterial, electrochromic particles, and ion producing particles in avacuum of about 10⁻⁴ torr with said mixture and said electrode beingspaced from one another by a distance of about l0 cm.
 14. The method ofclaim 13 wherein: said electrochromic material is a finely dividedanodic electrochromic material.
 15. The method of claim 14 wherein: saidfinely divided anodic electrochromic material is all the same.
 16. Themethod of claim 13 wherein: said finely divided electrochromic materialis a finely divided cathodic electrochromic material.
 17. The method ofclaim 16 wherein; said finely divided cathodic electrochromic materialis all the same.
 18. The method of claim 13 wherein: said electrochromicmaterial is a mixture of both finely divided anodic electrochromicmaterial and finely divided cathodic electrochromic material.
 19. Themethod of claim 18 wherein: said finely divided anodic electrochromicmaterial is all the same and said finely divided cathodic electrochromicmaterial is all the same.
 20. The method of claim 13 wherein: saidinorganic based solid material includes aluminum oxide.
 21. The methodof claim 13 wherein: said inorganic based solid material includestantalum oxide.
 22. The method of claim 13 wherein: said inorganic basedsolid material includes silicon oxide